17 October 2016 Deep proton writing with 12 MeV protons for rapid prototyping of microstructures in polymethylmethacrylate
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J. of Micro/Nanolithography, MEMS, and MOEMS, 15(4), 044501 (2016). doi:10.1117/1.JMM.15.4.044501
Deep proton writing (DPW) is a fabrication technology developed for the rapid prototyping of polymer microstructures. We use polymethylmethacrylate (PMMA) substrates, which act as a positive resist, for irradiation with a collimated 12-MeV energy proton beam. Using 12 MeV enables the irradiation of increasingly thick PMMA substrates with less conicity of the sidewalls compared to the lower energies used in previous work. A microhole of 47.7  μm diameter over a depth of 1 mm is achieved, leading to a maximum aspect ratio of 21∶1. The sidewalls of the irradiated structures show a slightly conical shape and their root-mean-square surface roughness is lower than 50 nm averaged over 72 measured areas of 56  μm×44  μm. This means that DPW components have optical surface quality sidewalls for wavelengths larger than 400 nm. Based on the trade-off among the sidewall roughness, conicity, and the development time, we determine that the optimal proton fluence for 12-MeV DPW in PMMA is 7.75×106  μm−2. Finally, we discuss some high aspect ratio microstructures with optical surface quality that were created with DPW to be used for a myriad of applications, such as micromirrors, microlenses, optofluidic devices, and high-precision alignment structures for single-mode optical fiber connectors.
© 2016 Society of Photo-Optical Instrumentation Engineers (SPIE)
Evert Ebraert, Berkcan Gökçe, Sandra Van Vlierberghe, Michael Vervaeke, Pascal Meyer, Markus Guttmann, Peter Dubruel, Hugo Thienpont, Jürgen Van Erps, "Deep proton writing with 12 MeV protons for rapid prototyping of microstructures in polymethylmethacrylate," Journal of Micro/Nanolithography, MEMS, and MOEMS 15(4), 044501 (17 October 2016). https://doi.org/10.1117/1.JMM.15.4.044501

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